JammedStab:
I thought you needed at least flaps 1 prior to this thread.
You might be thinking of the Barbie Jet, whose "on approach" requirements are a little different to the somewhat ageing "Queen of the Skies".
From the 777 FCOM:
The FMC transitions to "on approach" mode for any of the following conditions:
• the descent phase is active and flaps are out of up, or
• the airplane has sequenced the first waypoint (or FAXXX) of the active approach,
or
• the airplane is on a direct-to or intercept course-to the active waypoint and the
distance to go is less than 12 nm, or
• the missed approach point is the active waypoint and the distance to go is less
than 25 nm
The approach condition may be delayed if the flight crew manually inserts, bypasses,
or deletes an approach waypoint on the LEGS page.